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i88

TUNGSTEN STEELS

TABLE XI
Composition of Manganese Steels

No.
	C
	Si
	Mn
	P
	S

I .
	0-320
	0-311
	6-32    .
	0-077
	0-036


	0-585
	0-265
	9-61
	0-086
	0-042

3 •    •
	0-804
	0-280
	8-70
	0-034
	0-015

4 •     •
	1-085
	0-241
	12-24
	0-068
	O-OI2

TUNGSTEN   STEELS

Tungsten steels are very hard and serve specially for making tools,
permanent magnets, etc. Their analysis includes estimations of the
ordinary elements of steel and also of tungsten.

1. Determination of the Silicon and Tungsten.—When tungsten
steel is treated with nitric acid, the silicon present separates as silica and
the tungsten as tungstic acid. After weighing, the precipitate is treated
with hydrofluoric acid, the loss representing the silica and the remainder
the tungstic acid.

Procedure. 2-5 grams of the finely powdered sample are treated in a
covered dish with nitric acid (D 1-18), the solution being evaporated and
the residue ignited to decompose the nitrates and taken up in hydrochloric
acid. The liquid is then evaporated to dryness, the silica rendered insoluble
at 135°, as under 2, p. 172. The residue is moistened with cone, hydro-
chloric acid and then just sufficient hydrochloric acid (D 1-12) added to
dissolve the ferric oxide in the hot. The liquid is evaporated to a syrup,
allowed to cool, diluted with about double its volume of water acidified
with hydrochloric acid and, after a few minutes, filtered by decantation.
The precipitate is afterwards introduced on to the filter and washed with
water acidified with hydrochloric acid until the liquid passing through no
longer gives the reaction for iron with thiocyanate.1 After being dried,
the filter and precipitate are incinerated in a platinum crucible and the
residue ignited at not too high a temperature (not in the blowpipe flame)
and weighed.

To eliminate and estimate the silica, the weighed mixture of tungstic
acid and silica is treated with a little sulphuric acid and a few c.c. of hydro-
fluoric acid and the procedure indicated on p. 171 then followed.

The loss of weight gives the silica and this, multiplied by 0-4693 the
silicon ; the residue is the tungstic acid, multiplication by 0-7931 giving the
tungsten.

If the sample contains more than 10-15% °f tungsten, it is difficult
to attack with nitric acid and it is then advisable to have recourse to fusion
(see later: Ferro-tungsten).

1 A yellow ring of tungstic acid, difficult to remove merely by washing, is often
formed in the dish. This may be detached by gentle rubbing with a piece of filter paper
moistened with ammonia, the paper being then added to the rest of the precipitate.e water.